I never understood the idea that you're supposed to mellow as you get older. Slowing down isn't something I relate to at all. The goal is to continue in good and bad, all of it.
Another cause of change, one less noticeable but fundamental, is the modern growth of population closely connected with scientific and medical discoveries. It is interesting that the United Nations has set up a special Commission to study this question.
To be compared to Will Smith is probably one of the coolest things because that's who I came up admiring.